1. Field of the Invention
The present invention relates to an electrophotographic photo-receptor. In particular, the present invention relates to an organic electrophotographic photo-receptor including a novel μ-oxo bridged heterometal compound as a charge generating material.
2. Description of the Related Art
In an apparatus for image-forming in electrophotographic field such as a copying machine or a printer, an organic photo-receptor having sensitivity for a particular wavelength range generated from a light source of the apparatus has been used. Known organic photo-receptor includes a mono-layered form photo-receptor and a multi-layered form photo-receptor. The mono-layered form photo-receptor generally has a thin layer of binding resin, which contains charge generating material and charge transporting material dispersed therein. The multi-layered form photo-receptor generally comprises two layers, i. e., a charge generating layer containing a charge generating material and a charge transporting layer containing a charge transporting material.
Organic photo-conductive substances having sensitivity around a wavelength of 780 nm which is an oscillation wavelength range of a semiconductor laser have been noted as charge generating materials (CGM). A number of organic photo-condudtors (OPC) including such organic photo-conductive substances used as a charge generating material have been proposed. For example, organic photo-condudtors employing titanylphthalocyanine compounds as charge generating materials have been practically used. Organic photo-receptors having high sensitivity, high stability and good durability are strongly desired according with digitalization and speeding up of a copying machine or a printer.
Phthalocyanine compounds and naphthalocyanine compounds have various polymorph (form of crystalline structures) due to its frame structure, and have various electric properties caused by metal-free phthalocyanine/naphthalocyanine or the kinds of central metal of metal Phthalocyanine/naphthalocyanine. Also, the electric properties of the phthalocyanine compounds and naphthalocyanine compounds can vary greatly depending on a process for producing and treating these compounds. In addition, the electric properties of the compounds can vary greatly depending on stacking state even if they have the same structure. In particular, since the stacking states of an organic compound is determined by its polymorph and the polymorph can change state of electron, especially perturbation of n electron, polymorph is one of important features that significantly effects on properties of electronic material such as organic photo-receptor. Therefore, new polymorph has been searched.
Recently, charge generating materials having high sensitivity and high performance have been searched for adjusting for use of short wavelength of light sources due to prevalence of light-emitting diodes (LED) or for color laser-beam printers (LBP) OPC.
For example, with regard to a mixed crystal of two or more kinds of phthalocyanine compounds, Japanese Patent Kokai Publication No. Hei 2(1990)-272067 discloses a process for preparing a X-form metal-free phthalocyanine composition, which includes the steps of adding titanyl phthalocyanine to metal-free phthalocyanine in an amount of the same or less of metal-free phthalocyanine, and stirring the reactant to induce polymorph. Japanese Patent Kokai Publication No. Hei 4(1992)-351673 discloses an electrophotographic photo-receptor containing a mixed crystal comprising oxytitanium phthalocyanine and at least one kind of hydroxymetal phthalocyanine. Japanese Patent Kokai Publication No. Hei 8(1996)-67829 discloses a phthalocyanine mixed crystal with high γ property, which is prepared by dissolving at least two kinds of phthalocyanine compounds in acid; and adding the resultant solution to a mixture solution of water and an organic solvent having a dielectric constant of 20 or less to precipitate as the phthalocyanine mixed crystal. Japanese Patent Kokai Publication No. 2002-12790 discloses organic electrophotographic photo-receptor including a mixed crystal which comprises at least three kinds of phthalocyanine each having different central substance.
Japanese Patent Kokai Publication No. Hei 4(1992)-184452 discloses a coating composition containing titanyl phthalocyanine and multi-type derivative of phthalocyanine (e. g., μ-oxo bridged aluminum phthalocyanine and gallium phthalocyanine), and an electrophotographic photo-receptor using the same. Further, Japanese Patent Kokai Publication No. Hei 9(1997)-217020 discloses a μ-oxo aluminum phthalocyanine dimer having a new polymorph, and Japanese Patent Kokai Publication No. Hei 10(1998)-88023 discloses a μ-oxo gallium phthalocyanine dimer, and the dimers are used as an electrophotographic photo-receptor. In addition, Japanese Patent Kokai Publication No. Hei 7(1995)-295259 discloses an alkoxy bridged metal phthalocyanine dimer, and the dimer is used as an electrophotographic photo-receptor.
Japanese Patent Kokai Publication No. 2000-219817 discloses a photo-receptor containing a μ-oxo aluminum/gallium phthalocyanine dimer (PcAl—O—GaPc) with high sensitivity and high stability on using as organic photo-conductive material such as high gamma photo-conductive material. However, the phthalocyanine dimer described above has heterometal atoms which are able to have a valence of up to three, so the dimer is different from the compound used for an organic photo-receptor according to the present invention. In addition, the dimer is mixed compounds containing homometal dimer, so the dimer is different from the compound according to the present invention.